The present invention is in the field of film thickness measurement methods and film thickness measurement devices.
This invention relates to methods of measuring film thickness. More specifically, this invention relates to a capacitive measurement method useful in determining lubricant film thickness on substrates such as magnetic disks.
Perfluoropolyether lubricants currently used on magnetic thin-film rigid disks play a crucial role in protecting the head and disk surfaces. Uniformity of the lubricant film is critical for producing disks with consistent performance. Techniques to measure film thickness presently include X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, ellipsometry, and optical surface analysis. The first three such methods produce point measurements and require a substantial amount of time to properly map a surface. The fourth method, optical surface analysis, is best suited for determining a change in surface properties and is limited in vertical resolution of lubricant film thickness in comparison to other methods.
It is thus an object of the present invention to develop a method which can quickly, nondestructively, and accurately map lubricant film thickness and characterize lubricant depletion.
Although described with respect to the field of lubricant film thickness measurements, it will be appreciated that similar advantages of quick, non-destructive measurements, as well as other advantages, may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes capacitive film thickness measurement devices and measurement systems. The invention also includes machines or instruments using those aspects of the invention. The present invention may be used to upgrade, repair, or retrofit existing machines or instruments of these types, using methods and components known in the art.
The present invention additionally includes methods and procedures using the devices of the present invention. The methods and procedures of the present invention may be applied using procedures and protocols known and used in the arts to which they pertain.
In broadest terms, the present invention includes a film thickness measurement device comprising: (1) a rotation-capable platform for supporting a conductive substrate, the platform adapted to rotate at varying speeds; (2) a conductive probe located sufficiently near and above a conductive substrate on the rotation-capable platform, the probe adapted to move radially from sufficiently near the axis of rotation of the conductive substrate to sufficiently near the outer edge of the conductive substrate, and/or from the outer edge to the axis of rotation; (3) a capacitance-measuring device adapted to measure capacitance between the conductive substrate and the conductive probe; and (4) a force transducer adapted to measure friction and normal forces applied to the conductive probe. The conductive probe may be comprised of a commercial slider or a metal pin immersed in a contained liquid dielectric.
Also included in the present invention is, in broadest terms, a method for measuring film thickness, the method comprising the steps of: (1) placing a film-coated conductive substrate upon a rotation-capable platform, the platform adapted to rotate at varying speeds; (2) placing a conductive probe sufficiently near and above the film-coated conductive substrate, the probe adapted to move radially from sufficiently near the axis of rotation of the film-coated conductive substrate to sufficiently near the outer edge of the film-coated conductive substrate, and/or from the outer edge towards the axis of rotation; (3) rotating the rotation-capable platform at a predetermined speed of rotation; (4) measuring the capacitance between the conductive probe and the film-coated conductive substrate over at least one rotation at the current radial probe position; (5) moving the conductive probe radially a predetermined distance toward or away from the axis of rotation; (6) measuring the capacitance between the conductive probe and the film-coated conductive substrate over at least one rotation at the new radial probe position; (7) measuring the frictional force applied to the probe over at least one rotation at the new radial probe position; (8) continuing to move the probe in steps of the predetermined distance and measuring the capactitance and frictional force at those positions until all regions of interest of the film-coated conductive substrate have been measured; and (9) using the acquired measurements of capacitance and frictional force to calculate film thickness at each region of interest.
The method for measuring film thickness may additionally comprise the step of averaging capacitance measurements taken at each radial probe position. The averaged capacitance measurements may then be used to normalize the capacitance measurements taken at each radial probe position, whereby the effect of drift in capacitance may be minimized. Also included in the method may be the step of taking an independent measurement of film thickness using an appropriate method whereby the capacitance measurement may be calibrated.